High-level expression of the cytokine receptor-like factor 2 gene, CRLF2, in precursor B-cell acute lymphoblastic leukemia (pB-ALL) was shown to be caused by a translocation involving the IGH@ locus or a deletion juxtaposing CRLF2 with the P2RY8 promoter. To assess its possible prognostic value, CRLF2 expression was analyzed in 555 childhood pB-ALL patients treated according to the Acute Lymphoblastic Leukemia Berlin-Frankfurt-Münster 2000 (ALL-BFM 2000) protocol. Besides CRLF2 rearrangements, high-level CRLF2 expression was seen in cases with supernumerary copies of the CRLF2 locus. On the basis of the detection of CRLF2 rearrangements, a CRLF2 high-expression group (n = 49) was defined. This group had a 6-year relapse incidence of 31% plus or minus 8% compared with 11% plus or minus 1% in the CRLF2 low-expression group (P = .006). This difference was mainly attributable to an extremely high incidence of relapse (71% ± 19%) in non–high-risk patients with P2RY8-CRLF2 rearrangement. The assessment of CRLF2 aberrations may therefore serve as new stratification tool in Berlin-Frankfurt-Münster–based protocols by identifying additional high-risk patients who may benefit from an intensified and/or targeted treatment.

Sir2 is the most intensively discussed longevity gene in current aging research. Although, the gene encoding for a NAD+-dependent histone deacetylase initially was found to extend lifespan of various organisms ranging from yeast to mammals, serious doubts regarding its role in longevity have been expressed recently. In this study, we tested whether tissue-specific overexpression of Sir2 in the adult fat body can extend lifespan when compared to genetically identical controls. We also wanted to elucidate the mechanisms by which fat body Sir2 promotes longevity by studying the phenotypic and transcriptional changes in the fat body. We found that moderate (3-fold) Sir2 overexpression in the fat body during adulthood only can promote longevity in both sexes by roughly 13 %. In addition, we obtained transcriptional profiles elicited by this overexpression and propose a role for Sir2 in lipid droplet biology especially under conditions of starvation. Furthermore, our data do not support the idea of Sir2 mediating the response to dietary restriction (DR) because transcriptional profiles of fat bodies after DR or Sir2 overexpression do not match. This study provides additional independent evidence for the concept of Sir2 as a longevity gene and as a promising pharmacological target to cure age-related diseases.

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742 Further improvement of outcome in childhood acute lymphoblastic leukemia (ALL) could be achieved by identifying additional high-risk (HR) patients who then may benefit from an intensified treatment. In trial ALL-BFM 2000, the HR group was defined by inadequate initial response to induction treatment [poor prednisone response on treatment day eight (PPR), non remission on treatment day 33, and/or a high load of minimal residual disease (MRD, ≥10E-3) after 12 weeks of treatment (TP2)] and/or by positive cytogenetics for a t(4;11) or t(9;22). No MRD already on treatment day 33 defined standard risk (SR) patients, a measurable MRD at a low level characterized the intermediate risk (IR) group. Of importance, the majority of relapses occurred within this heterogeneous group of patients. In order to identify potential new stratification markers we earlier compared gene expression profiles of MRD resistance (HR) and sensitive (SR) ALL in a case-control setting (Cario et al, Blood 2005). Subsequently, we aimed at confirming the potential prognostic relevance of genes identified and their respective proteins in representative study populations. CD45 (also PTPRC, protein-tyrosine phosphatase, receptor-type, C) was one of these candidate genes. In order to assess its prognostic relevance, CD45 gene expression was first analyzed by quantifiable RT-PCR in a set of 555 precursor B-ALL (pB-ALL); its protein expression subsequently in 422 pB-ALL patients by flow cytometry. About one third of patients were included in both study sets. Normalization of protein expression was done by assessing the density of surface expression relative to its density on normal lymphocytes. The 90th percentile was used as a cut-off to distinguish a CD45-high from a CD45-low expression group in both analyses. In gene expression analysis we observed a significant association of a high CD45 expression with a high white blood cell count at diagnosis (WBC) (P = 0.0004), NCI-HR (P = 0.03) as well as presence of the MLL-AF4 rearrangement (P < 0.0001). Moreover, a high CD45 expression was associated with in-vivo treatment resistance as defined by MRD (P = 0.0025). Analyzing CD45 protein expression confirmed the association of a high expression with a high WBC (P < 0.0001), NCI-HR (P = 0.0002) as well as presence of the MLL-AF4 rearrangement (P < 0.0001). Moreover, although the association to treatment resistance was lower (P = 0.055), patients with a high CD45 expression had a significantly worse 5-years EFS probability of 62±8% compared to 82±2% for those in the low-expression group (P=0.002). Focussing on the IR group, patients with a high CD45 expression had a very poor outcome (EFS 45±15%) as compared to those with a low expression (EFS 86±3%, P < 0.0001). This effect was mainly related to a higher cumulative relapse incidence (55±16% vs. 13±3%, P < 0.0001). Of interest, no significant differences in EFS were seen in HR patients. Based on our results, consideration of CD45 protein expression may serve as additional stratification tool in BFM-based protocols to further refine true non-high-risk patients with a low risk of relapse by identifying additional patients at high relapse risk. Of importance, in view of the fact that CD45 expression was not prognostic in the high-risk group, patients with a high CD45 expression currently treated on non high risk arms, may potentially benefit from an intensified treatment in the HR arm. Disclosures: No relevant conflicts of interest to declare.